I get 99% of my magazines from Yahoo Japan auctions. When I was still buying a lot I would just browse the Ribon category (here!) and bid on whatever interested me. You will need to go through a deputy service like Shopping Mall Japan or Celga to have them bid/buy stuff on your behalf, so it does get expensive very quickly.
The paper in the older magazines is yellowed and soft but usually not brittle. The bindings are sturdy enough for me to open the books fairly wide to scan them. I think the newer magazines are more cheaply made than the older ones and probably won’t hold up as well in the long run. I think the newer books may also be bound differently, though I could be wrong.
As far as paperbacks vs magazines, I mostly buy the older magazines to see the pretty color art and to check out the work of the mangaka I’m not familiar with. Then I buy the tankoubon once I decide it’s something I want to read, though sometimes the older stuff can be hard to find. For newer manga, I have a subscription to Cookie because at one point I was following a bunch of series, but now I am so far behind on all of them (even though it switched to bimonthly somewhat recently) that I am probably going to cancel. It’s cheaper just to buy the individual titles I’m interested in since I’m going to buy those anyway. :P
I am so late in replying to this, but I was very pleasantly surprised to get it so early. Hopefully everyone else has gotten theirs by now.
I’ve been watching it off and on and it is actually a bit more over-the-top than I remembered. :P